You might want to check the battery health on those phones. When the battery gets doggy the performance is affected (to prevent app crashes and system crashes).

They can do a remote diagnostic to figure out where the issue is. Also try booting in safe mode. Hold down the left shift key while booting.

It does sound like a logic board issue though.

Just an idea. Copy all the data you can from that external drive to something else just in case that’s all you can get. Plug the external drive into the Mac with the bad drive. Connect the Mac to your network with a Ethernet cable, turn on the Mac while doing command option r combo when you see the Apple. Go to disk utility and format the external to hfs (it will wipe the disk). Exit disk utility and go to the install mac menu. once install on the external drive is complete restart while holding down the alt key and select the external. Boot off the external drive. Recover data by copying it to the external boot drive or another external you have. You may want to test the command option r first and I would disconnect the failing HDD during most of that process.

Did you try to go into the uefi setting to see if the keyboard was functioning as expected? This will eliminate any software issues with drivers and OS. you can go into the security/ setup password to type. If it fails it’s a hardware issue, if it works then it’s software (probably).

That was my first thought too. Regardless it’s got to be uefi/bios related as it’s across OSes

Try using pcpartpicker.com. You can do your build on the site and it will list the best deals for the components you choose. As a bonus it will check to see if there are some glaring incompatibilities at the same time.